introduction: the aim of this study was to compare the changes that occur in the danger zone (dz) after preparation of curved mesiobuccal (mb) canals of mandibular first molars with waveone instruments in two different movements [reciprocation (rcp) and counter-clockwise rotation (ccwr)] by means of cone-beam computed tomography (cbct). methods and materials: mb canals of 30 mandibular molars w...